Since the liquid crystal itself does not emit light, an external backlight source is required to realize the display in various Liquid Crystal Display (LCD) devices such as a liquid crystal display, a liquid crystal TV. The backlight source is divided into two types based on distribution locations: the side light type backlight source and the direct-type backlight source. The side light type backlight source is widely applied in the small size and medium size LCDs due to advantages of reduced number of required light-emitting devices, low cost and thin thickness.
FIG. 1 shows a partial sectional diagram of a side light type backlight module. The side light type backlight module includes, from down to up, a backboard 1, a light guide plate 2 and an optical membrane material 3 arranged above the backboard 1 in turn, a backlight source 6 arranged adjacent to a side face of the light guide plate 2 and a plastic frame 4 for fixing the light guide plate 2 and the optical membrane material 3. A display panel 5 is arranged above the backlight module. The light guide plate 2 is used to guide and conduct rays from a light-near end to a light-far end. Grid points are also printed on a lower surface of the light guide plate 2 which is opposite to a light exit face, so that an entire light exit face is uniform to form a surface light source which is provided to the display panel 5 for displaying.
However, since the light guide plate 2 is limited to materials and pattern adjustment, the light exit face of the light-near end emits more rays, and the picture is brighter; but the light exit face of a middle part and the light-far end emits less rays, and the picture is darker. This phenomenon is especially obvious for oversized products. Furthermore, there is a problem for the large-sized light guide plate 2 that the cutting of the light guide plate 2 and the making of the grid points are difficult.